This disclosure relates to single-photon avalanche diodes, their associated readout circuits, and, without limitation, to perimeter-gated single photon avalanche diodes, delay elements, hold-off circuits, quenching circuits, and reset circuits. Furthermore, this disclosure relates, without limitation, to single-photon avalanche diode arrays, pixels, and their associated readout circuits.
The background description provided below is for the purpose of generally presenting the context of the disclosure. The work described in this background section and aspects of the disclosure that may not otherwise qualify as prior art at the time of filing are neither expressly nor impliedly admitted as prior art against this disclosure.
Single-photon avalanche diodes are typically used for detecting weak and fast optical signals, and they are used in a wide variety of fields. For example, they are used in biomedical and biochemical assays to monitor fast-decaying optical signals originating from analytes. They are also used in light ranging applications as well as in telecommunications and quantum cryptography applications.
Readout circuits for single-photon avalanche diodes vary in architecture, and their design depends strongly on the application for which a detector is designed. However, one key feature common to virtually all readout circuits is the ability to quench an avalanche current in the single-photon avalanche diode and to optionally hold the single-photon avalanche diode in the quenched state for a period of time before returning it to its initial state.
Typical readout circuits are designed to hold the single-photon avalanche diode for a pre-determined period of time. For example, some readout circuit architectures include a monostable multivibrator that is configured to keep the single-photon avalanche diode biased at a quenching voltage for the duration of the unstable state of the multivibrator. In other typical implementations, a timing circuit may be used to provide a well-defined hold-off period.
Several drawbacks exist with respect to typical hold-off time generation circuits. For example, typical hold-off time generation circuits, such as those described above, may have a fixed delay time, and it may be prohibitive to include hardware for controlling these circuits in-pixel in detectors that include an array of single-photon avalanche diodes. Another drawback may be that typical hold-off time generation circuits do not provide the capability to generate a wide range of time delays at different resolutions, even when their resulting hold-off time is adjustable.